Four people have died after a plane and a helicopter crashed in mid-air over Buckinghamshire, according to a BBC report.
Two people were killed in each aircraft, Thames Valley Police said.
Police and the Air Accidents Investigation Branch (AAIB) said they have launched a joint investigation to establish the cause of the collision just after midday at Waddesdon Estate, near Aylesbury.
A Wycombe Air Park spokesman said both aircraft came from the airfield.
Supt Rebecca Mears, from Thames Valley Police, said she could not give any details of the identity or the genders of the victims at this stage and her “first priority” was the next of kin.
She said it was “too early to tell” what might have caused the crash.
The AAIB said the plane involved was a Cessna.
Emergency services were called to Upper Winchendon, close to Waddesdon Manor, at 12:06 GMT.